Method of producing phosphoric products



.acid and the product which is soluble in tively low' value METHQD OF PRODUCING PHGSPHUR-KC PROBUQTS Leroy H. Facer, Phelps Township, Ontario County, N. Y assignor, bynresne assignments, to Glen E. *Cooley, Schenectady, N. Y., Warren Dnnham Foster, Ridgewood, "N. 3., Halfdan Gregersen, New York, E21, -Magnus I. Gregor-sen, Engiewond, N. 5.,and Dana Lamb, New York, N. Y trustees No Drawing. Original application Italy 9, 1942, Serial No. 450,324. Divided and this application April 19, '1951,'Serial No. 221,932

17 Claims. (Cl. 7137,)

As is well known to practitioners of the fertilizer art,

the three major products of importance in any complete or mixed fertilizer (known in the trade as mixed-goods) are nitrogen (N), phosphorus (P205), and potash (K20). Few of these products are separately sold to farmers but are combined into completely or partially mixed tertilizers, either by their manufacturers or by intermediary establishments known as a dry mixers. The material most widely used as a source of phosphates, either in a mixedfertilizer or alone, is superphosphate. Superphosphate of usual concentration generally -is -made by treating ground phosphate rock with sulphuric or other strong mineral acid in order to convert the phosphate-in the rock, which is in a form in which it cannot be used 'bytheplant, to a form in which it can be so used.

rials used to furnish the nitrogenous and -potassic components of mixed fertilizers contain up to-fifty percent or even more available N or K20, respectively. Since fertiliz r is a'bulk product which in comparison with many other products of the heavy chemical industries is of'relaper ton, freight makes up arelatively 'large'proportion of the price that a farmer mustpay and its phosphatic components contribute more than their proportionate share to this tax. As freight rates increase inthe futurephosphaticproducts of low concentration become increasingly uneconomic.

As a result of these factors variouseliorts have been ma'de'to produce phosphorus-bearing products which are more concentrated. Such efforts have been'directed-along two general lines-known as heat processes and wet processes. Where electricity is available at a low cost-or =woulcl otherwise so to waste or for other reasons is used on an uneconomic basis heat processes have found: slight acceptance. "this invention and those related theretoare --nct:concerned with such w rtlternatively and to a generally uneconomic operations. presently much greaterwextent, socalled triple superphosphate, having a concentration of the. order of fifty percent P205, is produced by a -.wet

.process under which phosphate rock is acidulated with phosphoric acid. Such conventional .wet processes,

although cheaper per unitsthan heat processes, .soffar as known to me still cost much more terms of units of P205 less than ten percent in this country. is applied other than by superphosphate of regular per unit of P205. (In

concentration. Thus in spite of great saving of freight,

. object is achieved through the I produce phosphoric acid per se.

;reprocessed for .etfective use, or by Patented Mar. 27, 1956 high ,Cflpital, operating and material costs have prevented wideadoption ,of concentrated superphosphates.

Toreduce these costs I have developed a novel (wet) method of producing triple superphosphate, as is described and claimed in my companion application Serial Number 221,931 tiled April 19, 19 51, which like this application is a division of my co-pending application ,Serial ,Number.4-S O,324, filed July 9, 1942. My improved triple superphosphate is much less expensive in plant and operation than any other triple superphosphate known to inerand costsabout the same per unit of P205 as doconventional superphosphates of ordinary concentration. Even soitis more expensive per unit than is my improved superphosphate of ordinary concentration as described .andtclaimedin my co-pending application SerialN umber 432,350, filed February 25, ,1942, parent to my applicationSerial Number 450,324. One reason for this additional cost is the higher cost of phosphoric acid relatively .to sulphuric in terms of resulting salable output. .Superphosphates with a concentration of more than about 20 percent .PzQs cannot be made except with phosphoric .acid,, if generally available phosphatic materials are used. ,Foran explanation of conventional and my novelmethods ,of producing triple superphosphate see my said companion application.

An important object of this invention, therefore, is .provision of methods to produce phosphoric acidmore cheaply, in capital and operating costs, than has hereto- .foreheenpossible, ,sofar as I amaware. Another. closely related. object is toproduce a superphosphateof medium ,concentration, which for convenience herein only I call enriched .superphosphate, which meets a large part of the demandfor a concentrated superphosphate but .at a greatly reduced cost per unit. This second mentioned application of certain of related to those by which Phosphoric acidmade according to this inventionis highly useful for myenriched superphosphate and triple superphosphate but-is .notlimited to my (or any other) process of making triple or othersuperphosphate and can beemployed for .any

,mydiscoveries which are closely purpose. As a step in the productionof my enriched ,.superphosphate I make phosphoric acid in situ and then utilize this acid, together with additional sulphuric, .to produce :a superphosphate of from 24 to30 percent avail- .ablephosphoricacid. As a result of the practice of. these processes, Whether applied to phosphoric acid orenriched super phosphate, I secure a by-product which for convenience I call gypsum sludge, which is of great value inanovel processes andproducts in the fertilizerart, as is another object of this invention.

An important object of my invention isto produce both my enriched superphosphate and gypsum sludge without the use of concentrated phosphoric .acid and all .atgreatly decreased operating and capital costs. to produce phosphoric acid and triple superphosphate require a relatively large capital investment and can be undertaken only upon the basis of a large operation. Plants to produce my phosphoric acid and enriched superphosphate may be inexpensive and relatively small and are within the reach of a relatively small operator.

In my co-pending parent application, Serial Number 450,324,-filed July 9, 1942, I describe and claim other processes all depending upon processing a phosphatic or related component or one containing a metallic (minor) element-either by a direct use ofmaterials which. conventionally are either wasted or must be expensively the use of such materials in a manner. to produce at one .operationboth Plants a major product and a minor butimportant lay-product.

As in my parent application this invention is particularly and materials. Also as in my parent application and herein I consolidate what previously has been a series of separate manufacturing operations into one. Thus it is conventional in this art to complete the manufacture of phosphoric acid as one isolated operation, then transport the finished acid to a distant point and utilize it to make a more concentrated superphosphate, likewise as a separate and isolated operation. As described herein in connection with enriched superphosphate I accomplish a better result more cheaply by telescoping separate operations into one continuous process in one place. By the use of the principles of this invention, I avoid processes which are expensive in capital, materials, labor and other operating costs and in respect of my enriched superphosphate secure a product which is physically and chemically better than conventional.

After describing my novel methods of producing enriched superphosphate I shall present my related processes for making phosphoric acid as a separate article of commerce. Prior discussion of my enriched superphosphate will assist in an understanding of the related processes by which I produce phosphoric acid.

My enriched supcrphosphate contains between 24 and 30 percent available P205, depending upon the materials which are used. Triple superphosphate is not sold to the farmer as such except in relatively limited quantities but is manufactured by a very few large producers who sell it to manufacturers of superphosphate or dry mixers who combine it with other materials to make so-called high analysis fertilizers. With very few exceptions fertilizers of these analyses can be made from my enriched superphosphate. Triple superphosphate as sold to the manufacturer of mixed fertilizers ordinarily costs at least 50 percent more per unit of available P205 than does superphosphate of ordinary strength. The cost of my enriched superphosphate per unit of available P205 ready for sale to the farmer is little if any greater than that of ordinary superphosphate, although it may slightly exceed the cost of superphosphate manufactured in accordance with the economical processes described and claimed in my co-pending application Serial Number 432,350, filed February 25, 1942, parent to the parent hereof. This enriched superphosphate has the peculiar crop-producing capacity of the product of my said application Serial Number 432,350. While those producers who now use triple superphosphate bought from others to reinforce their own production of superphosphate of percent and less can not afford the capital and operating costs of a conventional plant making triple superphosphate for their use they can afiord a plant for my enriched superphosphate.

Dilute phosphoric acid is the basis of my enriched superphosphate, but I employ a novel process requiring much less apparatus and expense than the conventional, creating thereby a by-product for Which I have profitable use. I then use this phosphoric acid in combination with sulphuric acid in a conventional manner, in accordance with the teachings of the said parent of my parent application, in order to acidulate phosphate rock to produce superphosphate having as its available P205 the sum of that which I use as an acidulating agent and that which is rendered available by the process of acidulation of the phosphate rock.

I may acidulate phosphate rock with sulphuric acid in a normal manner to produce dilute phosphoric acid, or I may produce phosphoric acid in a novel manner de scribed later herein. Ordinarily a mixture of this rock and sulphuric acid is passed through three reacting chambers and then into a settling chamber from which phos phoric acid of approximately Baum is drained, the residue being a sludge of phosphoric acid and gypsum. According to the conventional process this sludge is washed, generally by a counter-current method, in a series of chambers often as many as seven in number, and the final Wash water used as a diluent for sulphuric acid which is employed to digest the rock to make the phosphoric acid. It will of course be understood that in the creation of phosphoric acid by the acidulation of phosphate rock sufficient acid must be provided to complete the conversion of the phosphorus of the rock to phosphoric acid and sufficient sulphate provided to combine with the calcium liberated from the phosphorus to produce calcium sulphate. Sulphuric acid accomplishes both these results. The purpose, therefore, of using this dilute phosphoric acid as a diluent is for convenience in adding to the total phosphoric acid that which is recovered from the gypsum and to make the mixture sufficiently fluid to facilitate the separation of the acid from the gypsum. Also, one quantity of water both washes one batch and dilutes the next. The percentage of P205 originally in the rock which remains after washing may exceed even 5 percent out of the original total of 33 percent (in a rock of 72 percent B. P. L.), or a loss of about 15 percent of the possible recovery.

In my process I may carry the washing only far enough to produce the minimum liquid necessary for the dilution of the mass to the point necessary for the separa tion of the phosphorus and the gypsum. It will be understood, however, that if desired I may proceed in the conventional manner. As a consequence if the washing is limited the gypsum sludge which remains after washing carries a relatively high percentage of phosphoric acid. As described in my said co-pending parent application and in my co-pending application Serial Number 222,536, filed April 23, 1951, I use this sludge in various advantageous and novel ways. It is of course to be understood that this production of a superphosphate by the use of a gypsumphosphoric acid sludge need not be carried out jointly with the production of my enriched superphosphate, although the production of certain of the materials for each may well be carried out together. After concluding the description of my novel enriched super phosphate I shall present my processes for making phosphoric acid per so, these processes being modifications of those just described.

At this point I have phosphoric acid of 30 Baum or 41 percent. For this process, I completely omit the usual and expensive step of concentrating this acid.

As well known in this art, concentrated phosphoric acid is diflicult to transfer, handle and store. I avoid such difiiculties by the use of a dilute acid. I use this acid as a diluent for strong sulphuric acid with which I acidu late phosphate rock in order to produce my enriched superphosphate. The ratio diluent to sulphuric acid is determined by the analysis of product which I wish to produce. By using phosphoric acid of 30 Baumas a diluent of sulphuric acid of from 60 to 66 Baum I am able to produce enriched superphosphate of from 24 to 30 percent available P205. Analyses of enriched superphosphate of less than 24 percent can be secured by the dilution of the sulphuric acid in part by water and in part by the phosphoric acid. The following examples are typical:

To produce one ton of my enriched supcrphosphate of 30 percent P205 1 may mix 955 pounds of ground phosphate rock of percent bone phosphate of lime, 440 pounds of 66 Baum H2804 and 676 pounds of 30 Baum H3PO4. Thereafter in the manner taught in my said co-pending parent applications I place the above mixture hot and steaming in a pelleting drum and coat with a hundred pounds of additional ground phosphate rock similar to that originally used. If desired, the en tire amount of phosphate rock may be added at one time, but I secure a product which is both physically and chemically more desirable if I add it in the pelleting drum. By adjusting the pitch of the drum and the amount of moisture in the product and the duration of rotation I can make pellets of any desired size from merely large grains upwardly. It is emphasized that the term pellets" therefore is to be understood to include such large grains,

which need not be round. It is of course understood that Number 432,350 and remove the mixture from the denor the like and-place anogheat orotherforrn of dehydration :isxto be applied :the drum and: that this pelleting process is i veryrapid.

' iTo: produce one ton of" enriched superphosphate' ofiz24 zpercent available phosphoric acid, I may mix 1200'pol1nds .ofphosphaterock of 72 percent bonephosphate of lime, .tpreferably 1100 poundsin the mixing panand 100 pounds vthereafter, .680 pounds of sulphuric-acid of 60 Baum .and 285 pounds of phosphoric-acidofBaum, pro .ceeding as above.

Astaught in the said parent-of myparent applicatiom Ivmay add nitrogen and potashto the mixing pan or I may add these substances tothe pelleting drum.

In order to enjoy the complete crop-producingadvantages of :my processes of producing superphosphatic' fer- :itilizers as described and claimedin-my co-pending parent .lapplications Serial Number 450,324and 432,350, itis necessary that my products after they have solidified after .the mixing operation, asfor-example in a den'or "blockor alonga screw conveyor,-be not heated: or devbydrated and that the waternecessary for crystallization Y be maintained available for the chemicalreactions which 1 are peculiar-to my product in its finished form. All forms of dehydration including vacuum-drying as by anautoclave or otherwise and even conventional-aerationas by repeated crane movements as well as actual heating-or" negatively stated the absence of substantially consistent and reasonably rapid cooling-tend to be destructiveof the chemical advantages of my product. For a full discussion of this phase of'the preferred practice of this-invention reference is made to my last previously mentioned co-pending application.

I have found the use of the above principles'valuable in one ofmy novel methods of producing ordinary superphosphate by use of coarsely groundzphosphate rockin a two-stage operation. A full description of claims'thereto will be foundin my co-pending' parent application Serial Number 265,921, filed January 10, 1952.

Alternatively in this and other examples presented throughout this application I may cause the mass -to-solidify in any desired and practicable manner, for exampleand .as taught in my said co-pending applications Serial 450,324. After solidification I it in a pelleting drum as describedand claimed'insaid last above mentioned application. Thereupon while the drum is revolving I add the remaining one hundred pounds of rock as a coating material during the'latter stage of the pelleting. The result is a dry and free-flow- --ing superphosphate of the characteristicsdescribed and claimed in my said co-pending application,-SerialfNum- 'ber 432,350.

Aspreviously stated herein prefer to produce-the phosphoric acid which I use for my enriched super-phosphate in a novel and related manner. Such phosphoric acid so produced, I wish to emphasize, may be employed independently of any fertilizer operation describedor claimed herein or in said companion; co-pending applications. This phase of this invention makes use of a-modification of the principles and processes-above described. One factor in the relatively high cost of making -phos -In the Since fine rock must be used,

Baum or below since otherwise penetration and ease of handling by making use of a two stage-process similar to thatmentioned above.

Iwuse phosphate rock ground to the'coarsest'degree -common inthe 'United 'States for themanufacturewof -snperphosphate, namely sixty 4 percentpassing through a" 6 hundred mesh :screen. l. Many manufacturers of superphosphate; however; in; :spite; of-itheadditional cost, grind i'tlreir .rock: much more finely. I illustrate-my' invention 5 by-wrock :ground so I-that eighty-percent -passes through such ascreen. I thereupon divide this-rockon the basis of coarsenesswof grinding. If the rock isof usual characteristics :the coarse component which remains on a hundredmesh screen will average about twentypercent :of the total. I thereupon place-this coarse rock in a first reacting chamber and add sulphuric acid of thema'ximum concentration -which .is available for use, say-forexample .60'-Baum. .iNo diluent is added. This concentrated .tacid rthoroughly-wets these coarse particles and actively begins the digestive process-but the whole'mass-is 'fiuid :andthe rockparticles so coarse-that there is no tendency to .ball. Mild agitation-keeps the solid particles' from settling to the-bottom-and hastens'the digestion of these -coarse particles by keeping their-surfaces exposedto concentratedacid,=as.=will be apparent to those skilled in'this art. After five'or ten minutesof'agitation I- add'what- --ever diluent, either water or dilutephos'phoricacid, is

-necessary to lower 'the concentration of theacid to approximately 54" Baum. "Thereupon I add the-remaining fine phosphate rock,- which is percent ofthe total, and'proceed inaccordance with the usual methodof making phosphoric acid. That is, to say, the mass ispassed through a'plurality of reaction chambers wherein the Wash-water is used as an added diluent, until-HsPOr of 30: 'Baum is secured. In a very small operation, 'the digestion can be completed in one chamber. The gypsum sludge preferably is washed only to the point which is economic and practicah'the sludge being employed as else- --where stated. "The resulting phosphoric acid is of approximately 30 Baum without any concentration and is-therefore immediately 'available for use in making 'the enrichedsuperphosphate which I have described hereinabove.

The concentration of the acidso; produced is sub stantially that resulting from the first washingoperation in the conventional wet process as in theDorrzprocess, other processes at this point secu'ring only about 20 -Baum. I may makefulluse ofall the phosphoriccon- --tent whichremains in the gypsum sludge in available form by carrying the washing further, as is'conventional inthe art. The product of this additional washing is of course more dilute than that previously secured. If a more-concentrated acid is 'desired 'I- merely'concentrate -"the-product of rny-process with or without the more thorough washing. I emphasize that coarse grinding and use of a highly concentrated acid much reduces the cost of production irrespective of the elimination of this-further washing. It is particularly to' benoted that for the most part phosphoric acid is produced at a point which requires transportation of sulphuric acid ormaterials therefor (or phosphate rock)for a considerable distance. The transportation of concentrated sulphuric .acid iobviously is cheaper than-transportation.,of"a-'dilute;-sulphuric acid. -As a practical matter even whendilute acid is employed it is-usually theproduct of'dilution on the spot of more, concentrated acid.

As previously describeda sludge of gypsum containing a quantity'of phosphoric acid, say fronrtwo tofour percent of the total,is a byproduct of the conventional and also of my novel processesthatproduce phosphoric v acid. As stated abovein orden to, save expense I may stop, the washing operation while considerably more than this two to four percent of this phosphoric acid remains in the sludge. No matterat what point I stop I have novel, important and profitable use for this gypsum sludge and all or its available phosphoric content, as-is described and claimed -in-=my companion co-pending-application, Serial Number 222,536,"filed Ap'rilj 23, '1951, likewise divisional from my parent application.

It will have been noted from the'foregoing portion-of thisvspecificat'ion that in processes described and claimed herein, I preferably separate phosphate rock which forms the base material in my operations on the basis of particle size. I apply the entire amount of acid necessary for acidulation of the entire end product to such coarse particles and thereafter add the fine particles to the acidic liquid-containing mass thus secured thereby completing the digestion. I make similar use of these principles in my said copending companion application relating to the making of triple superphosphate Serial Number 221,931, filed April 19, 1951, and also to my companion application Serial Number 265,921, filed January 10, 1952, rela-ting to superphosphatic products, both of said applications being like this division from my said parent appli' cation Serial Number 450,324.

Although I am presenting for purposes of illustration *only certain preferred embodiments of my invention it will be readily understood that changes may be made thcrein within the spirit of my invention and the scope of my broader claims. The advantages of this invention Will have been made clear from the above discussion and are reflected in the appended claims. These advantages include the production at a relatively low cost per unit of available phosphate of an enriched superphosphate made without the use of concentrated sulphuric acid which meets a large majority of the uses within the United States of a concentrated superphosphateand the production at a relatively low capital, operating and materials cost of phosphoric acid. Another advantage is the production as a by-product of a gypsum sludge of which I make novel use.

I claim:

1. A process of producing a superphosphatic fertilizer which comprises separating ground phosphate rock into two portions, one containing relatively coarsely ground particles and one containing relatively finely ground particles, mixing said coarsely ground particles with concentrated sulphuric acid, the ratio of all rock and acid being such that the unavailable phosphates of the rock will be converted into phosphoric acid, agitating the mixture sufliciently thoroughly to wet these coarse particles and to bogin the digestive process, adding to the mass a diluent to lower the concentration of the acid, adding the remaining portion of finely ground phosphate rock, agitating this mixture, separating the liquid phosphoric acid from the gypsum sludge substantially as soon as such separation can take place, mixing concentrated sulphuric acid and this phosphoric acid, adding such acid to ground phosphate rock of an amount such that said acid will convert its unavailable phosphate to available forms, and mixing said last mentioned rock and acid thereby forming an enriched superphosphate.

2. A process of producing a pelleted superphosphatic fertilizer which comprises separating ground phosphate rock into two portions, one containing relatively coarsely ground particles and the other containing relatively finely ground particles, mixing said coarsely ground particles with concentrated sulphuric acid, the ratio of rock and acid being such that the unavailable phosphate of the rock will be converted into phosphoric acid, agitating the mixture sufficiently thoroughly to wet these coarse particles and to begin the digestive process, adding to the mass a diluent to lower the concentration of the acid, adding the remaining portion of finely ground phosphate rock, agitating this mixture, separating the liquid phosphoric acid so formed from the gypsum sludge substan tially as soon as such separation can take place, mixing concentrated sulphuric acid and this phosphoric acid, mixing said combined acid with ground phosphate rock, and directly passing the mass so formed to a revolving drum wherein it is formed into pellets, and thereafter retain ing in the cured product as water of crystallization substantially all of the moisture present at the beginning of the pelleting operation.

3. ,A process of producing a pelleted superphosphatic,

fertilizer which comprises separating ground phosphate rock into two portions, one containing relatively coarsely ground particles and the other containing relatively finely ground particles, mixing said coarsely ground particles with concentrated sulphuric acid, the ratio of rock'and acid being such that the unavailable phosphate of the rock will be converted into phosphoric acid, agitating the mixture sufliciently thoroughly to wet these coarse particles and to begin the digestive process, adding to the mass a diluent to lower the concentration of the acid, adding the remaining portion of finely ground phosphate rock, agitating this mixture, separating the liquid phosphoric acid so formed from the gypsum sludge substantially as soon as such separation can take place, mixing concentrated sulphuric acid and this phosphoric acid, mixing said combined acid with ground phosphate rock, and forthwith rolling said material upon itself whereby it is formed into pellets, and thereafter retaining the cured product as water of crystallization substantially all of the moisture present at the beginning'of the pelleting operation.

4. A process of producing a superphosphatic fertilizer which comprises separating ground phosphate rock into two portions, one containing relatively coarsely ground particles and one containing relatively finely ground particles, mixing said coarsely ground particles with concentrated sulphuric acid and agitating said mixture until the coarse particles are thoroughly wet and the digestive process is begun, the ratio of the rock and acid being such that the unavailable phosphate of the rock will be converted into phosphoric acid, thereafter adding sufficient diluent to lower the concentration of the acid to the order of 54 Baum, adding the remaining portion of finely ground phosphate rock, agitating this 1 the liquid phosphoric acid from the' mixture, separating gypsum sludge when it is of the order of 30 Baum, a liquid being added so to reduce the concentration and to make separation practicable, mixing phosphoric acid so formed and sufiicient concentrated sulphuric acid to re duce the mixture of phosphoric and sulphuric acid to the order of at least 56 Baum, and mixing ground phosphate rock with the mass so formed thereby transforming the unavailable phosphorus of the rock to available forms, thereby forming an enriched superphosphate without the use of phosphoric acid except that formed in the operation as above set out.

5. A process of producing a superphosphatic fertilizer which comprises separating ground phosphate rock into two portions, one containing relatively coarsely ground particles and one containing relatively finely ground particles, mixing said coarsely ground particles with concentrated sulphuric acid of the order of 60 Baum and agitating said mixture until the coarse particles are thoroughly wet and the digestive process is begun, the ratio of the rock and acid being such that the unavailable phosphate of the rock will be converted into phosphoric acid, thereafter adding sufficient diluent to lower the concentration of the acid to the order of 54 Baum, adding the remaining portion of finely ground phosphate rock, agitating this mixture, separating the liquid phosphoric acid from the gypsum sludge when it is of the order of 30 Baurn, a liquid being added so to reduce the concentran'on and to make separation practicable, mixing said phosphoric acid so formed and concentrated sulphuric acid of the order of at least 60 Baum, and mixing ground phosphate rock with the mass so formed thereby transforming the unavailable phosphorus of the rock to available forms, thereby forming an enriched superphosphate without the use of phosphoric acid except that formed in the mixing operation as above set out.

6. A method of producing a pelleted superphosphatic fertilizer which comprises dividing ground phosphate rock into two portions, one portion comprising relatively fine particles of which an amount of the order swindle of eight "percent will pass "through'a screen 'with 100 meshes to" the inch" andthe other "portion of-d-el'atively coarse" particles which will "not pass through such a screen, mixing' saidcoarse-patticles'with concentrated sulphuric' acid of the order of 60 Baum and agitating saidmixtureuntil the coarse" particles are thoroughly wet and'th'edigestiv'e process is begun, thef'ratio of 'rock and acidbeingsuch that the unavailable phosphate of the roclc will be conver'ted to phosphoric acid, thereafter adding sufficient diluent'to lowerthe concentration of theacid "to the 'orderof 54 Baum and adding the fine particles 'which make up the remainder of said phosphate rock}separatingthe"phosphoric acid so formed from th'ej'gypsum sludge when it is of a concentration of the"or der30"Baum, a liquid being ad de d'so to reduce -"the concentration and make separation practicable, mixingsaidphosphoric acid 'sojformed and concentrated sulphuric ac'id'of the order' of at least 60 Bau1n,'mixin g ground' phosphate rock with the acid so formed thereby transforming-the unavailable phosphorus of the rock"-to' availableforms, and directly passing the mass so formed to a revolving drum wherein it is formedinto pellets."

7. A'method' of producing a pelleted superphosphatic fertilizen'which comprises dividing ground phosphate rockintotwo portions, one portion comprising relatively fine particles of which an amount of the 'order of 80 percent Will pass through a screen with IOOmeshes to the square inch andt he other portion of relatively coarse particles which will notpass through such a screen, mixing saidcoarse particleswith concentrated sulphuric acid and agitatingsaid mixture until the coarse particles are th tfroii'ghly wet 'and the digestive process is begun, the ratio of rock and acid being such that the'unavailable phosphate of the rock' willbe" converted to phosphoric acid," thereafter'adding sufficient' diluent to lower the concentration of the acid to the order of srnsumana addin'g th'fine particles which make up the remainder of said phosphate-rock, separatingthe phosphoric-"acid so formed from the gypsumsludge when'it is of a concentration of theorder of Baum,--a liquid being added so toreduce the concentration and mak et'sep' ara'tion practicable," mixing saidphosphoric *acid so formed-and sulphuric acid ofsufii c'ient concentrationto produce'a combination of phosphoric and sulpliuricacid of at least 56" Baum, mixing ground phosphate rock with-the acid so formed thereby transforming'the 'unavailable' phospho'rus' of 'the'rockto available forms; and directly passing the-mass so formed to a revolvingdrnm wherein it isformed into pellets.

8.' A process of manufacturing a pelleted enriched superphosphatic fertilizer 5 which comprises 5 using 'dildte phosphoric acid to 'dilute concentrated sulphurioac'id'; dividing ground phosphate rock into a major and a m-inor portion, mixing said major portion of said phosphate rock and su'fficient quantityof the'said combined acid to convert to 'ava'il'able form the unavailable phosphates of said entire quantity of rock, the relative quantity of rock" in said major'portion being such as to result :in :a plastic mass after the combined acid has been mixed therewith, immediately passing such over-acidulated plastic mass into a rotatable pelleting drum, and rotating said drum thereby forming embryo pellets, and in a late stage of the pelleting operation adding said minor portion of said rock to the drum as it is rotated so that said minor portion adheres to and coats the embryo pellets and utilizes their remaining acidic component to acidulate such rock coating so that the identity of the pellets is thereafter maintained thereby, said entire pelleting operation being conducted under conditions such that the heat of reaction is dissipated readily and with substantially no evaporation of the water originally prescnt.

9. A process of manufacturing a pelleted enriched superphosphatic fertilizer which comprises using dilute phosphoric acid? to dilute concentrated sulphuric acid, dividinggroundphosphate rock into a major'and"a"miiio'r portion,'mixingsaidmajor portion of said phosph rock and"suflicienfqtiantity'ofthe s'a'id combined acid tweenvert" to 'availableform' the unavailable phosphates of said entire quan'tity 'of rock, the relative quantity ofro'ck in said major portion being such as to result ina"plastic mass-after" the combined acid has be en' mixed therewith, immediately" rolling" such over-acidulated plastic m'a'ss upon itself thereby'forming embryo'p'ellets and ma late stage of such pell'eting operation adding said minorpon tiori'of saidjrock'to'themass'as'it is rolled tip'onitself so that said'minor portion adheres to and coats'the embryo pellets and utilizes their remaining acidic componentto acidulate such rock coating so that identity of the pellets. is thereaftermaintained thereby, said entire pelleting'oper atio'n being 'co'nductedunder conditions such'thatth'e' head of reaction is dissipatedreadily and with substantially no evaporation of the Water originally present; p

10. A process of manufacturing a pelleted super'phes pliatewhi'c'h comprises using'phosphoric acidof a conced tration of the orderof 30 'Baum to dilute sulphuric acid; dividing phosphaterock into a major and minor portion, mixingthe rock of said majorpor'tion and allof the acid so: formed, the concentratio'nand' amount of this com bined acidinrelationto the phosphate rockof both portions' b'eing 'such' that no more "and no other wateris present than that required in the acidulation reactioiitoproduce "superphosphate and to furnish substantially all of -the'water'"evaporated by thenatural heat of reactio and all of tliew'ate'rj'of crystallization"required fol-"the substantially 'cornplete"hydration' of'the end product; directly'pa'ssing' the massso' formed with"'the'addition of said mi'norpo rtion of phosphatejrock to a revolving'drurii wherinit is termed into pellets, thereby eembinin 'rthe remaining-freeac'id and the'l'ast'added phosphate rock as superphosphate andeonverting the entire mass to a dry and non coale's'centcondition thereby retaining in the cured productas water of crystallization substantially all of "the original moisture which was actually present at the beginnihgef thepelletin ie eratien;

l1. Aproce'ssof manufacturing phosphoric acid which comprises" dividingground phosp'hate'rock into a minor portiohconsisting'of'particles"which are relatively coarse and a rnajor portion" consistirigof particles Which'are rela'- tively fine, mixing said minor" portion consisting of the coarsepa'rticles' with sui iicient relatively concentrated sulph'uric acid to boriV'er'tall of the :iinavailable' phosphate of bothpdrtions tophospheric acid; addii1gto the ac'idulated coarse rock sufiicieint diliient so that when the major por tion'consistingofthe fine" particles is added thereto there will 'be'e'nou'gh moisture "to reach all articles thereof, adding 'saidin'ajor portion," and after additional dilation separating the liquid acid so formed from the gypsum sludge.

processor manufacturin particulate sup'e'r'ph'os rtilizer which comprises? grinding a predet'e'r' mined quantity' of"phosphate rock; dividing said 'grou'nd rock into a major and afminor'portioni mixing concentra'te'd sulphuric acid and dilute phbsp'horic'acidof desired concentrations" to forlrifi'ddriibined'acid;:mixing and react: in prtietrmined"qua tity ofsaid combined acid with saidmajor p'd'rt'ionof thds'aid ground phosphate rock, the predetermined amount of combined acid being the amount sufficient to react with all of the said predetermined quantity of ground phosphate rock, and in excess of the amount sufiicient to react with said major portion of said phosphate rock, and the concentration of the said combined acid being sufficiently high to limit and control the amount of water present to that required by complete reaction of the entire predetermined quantity of ground phosphate rock and the entire predetermined quantity of said combined acid and to furnish water of crystallization of the snperphosphatic fertilizer produced after loss of water evaporated by the natural heat of reaction; disinte- 11 grating the mass formed by said mixing and reaction of said combined acid and said major portion of said rock to form disintegrated small particles-which are chemically active and over-acidulated; subjecting said disintegrated smallparticles to movement to form coalesced larger particles of desired size; and thereafter adding the said minorportion of said ground phosphate rock to coat the said coalesced larger particles, thereby reacting said minor portion of the said ground rock with the said excess quantity of combined acid to form substantially dry, coalesced particulate superphosphatic fertilizer.

13. A process of manufacturing particulate superphosphatic fertilizer which comprises dividing a predetermined quantity of ground phosphate rock into a major and a minor portion; mixing concentrated sulphuric acid and dilute phosphoric acid of desired concentrations to form a combined acid; the concentration of the said combined acid being such as to supply not more than the amount of water required in the entire acidulation reaction, while furnishing the amount of water evaporated by the natural heat of reaction and the amount required to furnish substantially the full amount of water of crystallization for the completely hydrated yet dry final product; mixing said major portion of ground phosphate rock and the entire amount of said combined acid necessary to form a super phosphatic fertilizer from said entire predetermined quantity of ground phosphate rock, thereby producing an overacidulated, moist, essentially solid mass which can be readily handled and which is disintegra'ble in the manner of ordinary superphosphate; disintegrating said mass into small particles; further processing the resulting small particles without the addition of external heat under conditions avoiding any substantial evaporation so as to obtain a dry final product, said further processing including adding to the outside surfaces of the disintegrated particles while still moist and overacidulated, the said minor portion of the ground phosphate rock, causing adherence of said added rock to said moist outside surfaces and a chemical bonding thereto, to produce a substantially dry, particulate superphosphatic fertilizer.

14. A process of manufacturing substantially dry, particulate superphosphatic fertilizer which comprises: dividing ground phosphate rock into a major portion and a minor portion; diluting sulphuric acid of a concentration on the order of from about 60 to about 66 Baum with phosphoric acid of a concentration on the order of about 30 Baum to form a combined acid, the concentration of the combined acid being such as to supply not more than the amount of water required in the entire acidulation reaction, while furnishing the amount of water evaporated by the natural heat of reaction and the amount required to furnish substantially the full amount of water of crystallization for the completely hydrated yet dry final product; mixing said major portion and the entire amount of said combined acid necessary to form a superphosphatic fertilizer from both said major and said minor portions of said phosphate rock, thereby producing an over-acidulated, moist, essentially solid mass which can be readily handled and which is disintegrable in the manner of ordinary superphosphate; disintegrating said mass into small particles; further processing the resulting small particles without the addition of external eat under conditions avoiding any substantial evaporation so as to obtain a dry final product, said further processing including adding to the outside surfaces of the disintegrated particles while still moist and over-acidulated, the said minor portion of the ground phosphate rock, thereby causing adherence of said added rock to said moist outside surfaces and a chemical bonding thereto, to produce substantially dry, particulate superphosphatic fertilizer.

15. A process of manufacturing phosphoric acid which comprises dividing ground phosphate rock into a minor portion consisting of particles which are relatively coarse and a major portion consisting of particles which are relatively fine, mixing said minor portion and sufficient rela tively concentrated sulphuric acid to convert all of the unavailable phosphate of both portions to phosphoric acid, adding to the acidulated coarse rock suflicient aqueous diluent so that when the major portion consisting of the fine particles is added thereto there will be enough moisture to reach all particles thereof, adding said major portion of said rock and agitating said mixture, adding only sufficient additional aqueous diluent so that the liquid acid so formed may be separated from the gypsum sludge, and so separating said acid.

16. A process of manufacturing phosphoric acid which comprises dividing ground phosphate rock into a minor portion consisting of particles which are relatively coarse and a major portion consisting of particles which are relatively fine, mixing said minor portion and sufiicient sulphuric acid of a concentration of the order of 56 Baum or greater to convert all of the unavailable phosphate of both portions to phosphoric acid, adding to the acidulated coarse rock sufiicient aqueous diluent so that when the major portion consisting of the fine particles is added thereto there will be enough moisture to reach all particles thereof, adding said major portion of said rock and agitating saidmixture, adding only suflicient additional aqueous diluent so that the liquid acid so formed may be separated from the gypsum sludge, and so separating said acid.

17. A process of manufacturing phosphoric acid of a concentration of substantially 30 Baum which comprises dividing ground phosphate rock into a minor portion consisting of particles which are relatively coarse and a major portion consisting of particles which are relatively fine, mixing said minor portion consisting of the coarse par ticles with sufficient sulphuric acid of a concentration of the order of 60 to 66 Baum to convert all of the unavailable phosphate of both portions to phosphoric acid, adding to the acidulated coarse rock sufficient aqueous diluent so that when the major portion consisting of the fine particles is added thereto there will be enough moisture to reach all particles thereof, adding said major portion of said rock, agitating said mixture, adding only sulficient additional aqueous diluent so that the liquid acid so formed will be of aconcentration of the order of 30" Baum, and separating said acid from the gypsum sludge.

References Cited in the file of this patent UNITED STATES PATENTS 1,604,359 Larison Oct. 26, 1926 2,015,384 Nordengren Sept. 24, 1935 2,106,223 Nordengren Jan. 25, 1938 2,136,793 Gabeler et a1. Nov. 15,1938 

12. A PROCESS OF MANUFACTURING PARTICULATE SUPERPHOSPHATIC FERTILIZER WHICH COMPRISES: GRINDING A PREDETERMINED QUANTITY OF PHOSPHATE ROCK; DIVIDING SAID GROUND ROCK INTO A MAJOR AND A MINOR PORTION; MIXING CONCENTRATED SULPHURIC ACID AND DILUTE PHOSPHORIC ACID OF DESIRED CONCENTRATIONS TO FORM A COMBINED ACID; MIXING AND REACTING A PREDETERMINED QUANTITY OF SAID COMBINED ACID WITH SAID MAJOR PORTION OF THE SAID GROUND PHOSPHATE ROCK, THE PREDETERMINED AMOUNT OF COMBINED ACID BEING THE AMOUNT SUFFICIENT TO REACT WITH ALL OF THE SAID PREDETERMINED QUANTITY OF GROUND PHOSPHATE ROCK, AND IN EXCESS OF THE AMOUNT SUFFICIENT TO REACT WITH SAID MAJOR PORTION OF SAID PHOSPHATE ROCK, AND THE CONCENTRATION OF THE SAID COMBINED ACID BEING SUFFICIENTLY HIGH TO LIMIT AND CONTROL THE AMOUNT OF WATER PRESENT TO THAT REQUIRED BY COMPLETE REACTION OF THE ENTIRE PREDETERMINED QUANTITY OF GROUND PHOSPHATE ROCK AND THE ENTIRE PREDETERMINED QUANTITY OF SAID COMBINED ACID AND TO FURNISH WATER OF CRYSTALLIZATION OF THE SUPERPHOSPHATIC FERTILIZER PRODUCED AFTER LOSS OF WATER EVAPORATED BY THE NATURAL HEAT OF REACTION; DISINTEGRATING THE MASSFORMED BY SAID MIXING AND REACTION OF SAID COMBINED ACID AND SAINDMAJOR PORTION OF SAID ROCK TO FORM DISINTEFRATED SMALL PARTICLES WHICH ARE CHEMICALLY ACTIVE AND OVER-ACIDULATED; SUBJECTING SAID DISINTEGRATED SMALL PARTICELS TO MOVEMENT TO FORM COALESCED LARGER PARTICLES OF DESIRED SIZE; AND THEREAFTER ADDING THE SAID MINOR PORTION OF SAID GROUND PHOSPHATE ROCK TO COAT THE SAID COALESCED LARGER PARTICLES, THEREBY REACTING SAID MINOR PORTION OF THE SAID GROUND ROCK WITH THE SAID EXCESS QUANTITY OF COMBINED ACID TO FORM SUBSTANTIALLY DRY, COALESCED PARTICULATE SUPERPHOSPHATIC FERTILIZER. 